A correction circuit for correcting mainly (i) residual misconvergence due to the magnetic field distribution design in a deflection yoke installed on a picture tube, (ii) irregularities during the winding of a coil, (iii) processing variances among the deflection yokes, or (iv) variances when a CRT (cathode ray tube) is adjusted to the DY (deflection yoke) in an ITC (integrated tube components) system, is employed on a printed board. This correction circuit comprises variable resistors and the like.
In order to ensure the security of the user and the safety of the product components (such as circuit components and terminals), a terminal board cover made of an insulating material such as resin is installed on the printed board, so that the user cannot directly touch the terminals on the printed board. Furthermore, through holes are employed on the terminal board cover above the variable resistors, which are components of the correction circuit on the printed board, so that a stick-shaped tool for adjusting the variable resistors (called "adjustment tool" below) can be inserted from outside the terminal board cover to adjust the variable resistors.
As is shown in FIG. 18, usually one through hole 7 is employed separately for each adjustment portion 6, so that the adjustment tool is guided smoothly to the adjustment area 6 of the variable resistors without being deviated from a position directly above the variable resistor. Furthermore, when several (in this prior art example: two) adjustment regions 6 for variable resistors are located closely together, a slender through hole 7, which openly connects the regions above the adjustment areas 6, is employed in the terminal board cover.
However, in the prior art employing separate through holes for each adjustment area of a variable resistor as discussed above, the position, distribution and relative position of the through holes cannot be determined precisely when the variable resistors are adjusted, because all the through holes have roughly the same circular shape. Consequently, there was the problem that after the adjustment tool has been extracted from a through hole and is about to be inserted into the next through hole, the next through hole has to be found, and some time is required to locate the position of the next through hole.
Furthermore, when employing slender through holes, which openly connect the regions above several adjustment areas located closely together, it is easy to deviate from the intended adjustment area for a variable resistor, because it is difficult to point the adjustment tool exactly at the intended adjustment area of several adjustment areas for variable resistors, so that this configuration also is hard to adjust.